A Cambodian psychologist told Khmer Rouge tribunal judges on Monday that the defendant, Duch, did not have “mental problems” enough to lead him into the revolution and his eventual role as chief of the regime’s killing machine, Tuol Sleng prison.

Duch, whose real name is Kaing Kek Iev, had testified that the loss of a girlfriend and a bicycle, combined with arrests of friends under the Lon Nol regime, had lad him to the Khmer Rouge.

Dr. Ka Sun Bunnath, a professor at the University of Science and Health, in Phnom Penh, told the court Duch had managed as a successful math teacher before joining the guerrillas, and so did not have insurmountable mental problems.

His view was supported by another expert, Francoise Sironi-Guilbaud, a French psychologist.

Meanwhile, 28 civil parties boycotted Monday’s hearing, following a decision by the court last week that they would not be allowed to question Duch regarding his personal character.